It is previously known to provide machines with emergency brakes which, should a dangerous situation suddenly arise, can be brought into operation by means of a brake actuating device. In the case of motor saws there is used, inter alia, a type of band brake having a brake band or strap placed around, for example, a clutch drum, the outside of which drum serves as a friction surface for the brake band. Under normal sawing conditions, the brake band extends loosely around the drum and does not affect the rotation thereof. Upon the activation of an activator, which may comprise a spring-tensioning device and a detachable latch means for releasing the spring, the band is drawn tightly around the drum, causing the saw chain to stop immediately. An emergency brake of this type is known from the U.S. Pat. No. 3,290,871. On present-day motor saws there is mounted adjacent the carrying handle of the saw a protective structure which is connected to the band brake actuating device, the intention being that should the saw throw, the hand of the saw operator will be thrown from the carrying handle against the protective stirrup structure, to activate said device. Since it is imperative that the brake is applied immediately the saw throws, it is obvious that precious time is wasted with this known construction before the protective stirrup structure is activated. Moreover, with the known construction the brake is not applied should the saw operator retains his grip around the carrying handle, or if, at the moment of the throw, the saw is held in a position such that said hand does not strike the protective stirrup.